With the development of display technologies, display devices such as liquid crystal display panels (LCD), organic electroluminescent display panels (OLED) and electronic papers are well known. Thin film transistors (TFTs) are provided in the above-mentioned display devices to control pixels to be turned on or turned off. TFTs are essential components to the pixel circuits of the liquid crystal display panels, and the organic electroluminescent display panels, and play a significant role. Therefore, many experts and scholars in the industry are attracted to continuously improve the design and preparation of TFT, so as to further improve the quality of displayed images.